The instant invention relates to a magnetically operated AC switching device, such as an AC contactor, and more particularly to an AC device which exhibits slight delay characteristics on dropout.
It has been found that for some electrical switching applications in the computer industry and in other industries, slight delay characteristics on dropout are desirable. More specifically, it has been found that for some applications it is desirable for a contactor to be operable to maintain a circuit in an electrically connected or closed condition for an instant after the electrical power to the contactor has been interrupted or shut off. In the computer industry a delay feature of this type is desirable for some contactor applications in order to permit safe shutdown of equipment energized through contactors in cases of power failure or serious "brownout" conditions. In this regard, a slight delay-on-dropout provides ample time to permit a safe shutdown of computer equipment without resulting in the loss of information and programming stored in memory, whereas without this feature data stored in the computer memory can be permanently lost.
Heretofore, DC contactors having delay features have been available and have sometimes been used in the above-described applications where delay features have been required. The heretofore known DC contactors have comprised separate DC pickup and holding windings, the pickup windings being of substantially greater strength than the holding windings and being operable for closing the contacts of the contactors, and the holding windings being operable for maintaining the contacts in the closed positions thereof. Contactors of this type have further comprised capacitors electrically connected in parallel across the holding windings thereof to provide the necessary delay features and have included switches for deenergizing the pickup windings thereof once the respective contacts of the contactors are in engagement to prevent burnout of the pickup windings, which draw substantial amounts of current. Unfortunately, however, the mechanical malfunction potential of the DC pickup winding switches has been a major drawback in contactors of this type and has frequently resulted in pickup winding burnout.
AC contactors have generally proven to be more reliable than DC contactors; however, AC contactors with effective delay-on-dropout characteristics have heretofore been unavailable. While attempts have been made to provide delay characteristics by mechanically delaying the opening of the contacts in AC contactors with dash pots or the like, the use of such mechanical devices has been ineffective. Specifically, mechanical delay components of this type have merely functioned to slow the movement of the contacts of the contactors and have therefore resulted in undesirable contact arcing. What is actually desired in this regard is a delay feature which initially delays the movement of contacts without thereafter impeding the movement of the contacts.
The reason that AC contactors in general are more reliable than DC contactors is that they do not require mechanical switching components in order to prevent pickup winding burnout. In this regard, when an AC contactor is energized, it initially draws a relatively large "inrush" current which creates a large magnetic field, whereby the armature of the contactor is magnetically attracted to the magnet thereof to close the contacts of the contactor. However, after the armature has been moved so that it is adjacent the magnet of the contactor, the current draw of the winding naturally decreases substantially to a low "sealed" current level which is required to keep the contactor in the closed position thereof but which can be maintained indefinitely without burnout. This is a natural phenomenon of AC contactors which permits the same winding to be used as both a pickup winding and a holding winding so that mechanical switching components are not necessary. It has, however, heretofore been impossible to provide electrical delay features in AC contactors of this type using capacitors since capacitors are only operable with DC voltage.
The instant invention provides an AC contactor which exhibits delay characteristics on dropout and which is therefore effective for use in the computer industry and other industries in applications where delay-on-dropout is necessary. Contactors of the type with which the instant invention are concerned comprise a contactor body made of an electrical insulating material, first and second fixed contacts mounted on the body, a fixed magnetically responsive element on the body, a movable magnetically responsive element on the body biased to a first position of spaced disengagement from the fixed element but movable to a second position of engagement therewith, and first and second movable contacts mounted in electrically insulated relation on the movable magnetic element for movement therewith between a position wherein they are in engagement with the first and second fixed contacts, respectively, and a position wherein they are in spaced disengagement from the fixed contacts. The contactor of the instant invention further comprises an AC pickup winding mounted on one of the magnetically responsive elements for effecting the magnetic energization thereof upon electrical energization of the pickup winding with an AC power source, and a DC holding winding mounted on one of the magnetically responsive elements for maintaining the movable element in the second position thereof. The contactor also comprises a capacitor electrically connected across the holding winding and a rectifier electrically connected across the holding winding in parallel with the capacitor for supplying DC power to the holding winding and the capacitor from the AC power source. Accordingly, the contactor is completely energizable from the AC power source and uses AC power for the pickup winding thereof but includes a rectifier for providing DC power to the holding winding thereof. As a result, the advantages of AC contactors and DC contactors are combined in a single contactor which uses both AC and DC power for the operation thereof but which is energizable from an AC power source.
In the operation of the contactor, the AC pickup winding thereof initially draws a substantial amount of current until the movable magnetically responsive element thereof is moved to a position of engagement with the fixed magnetically responsive element whereupon the power consumption of the AC pickup winding is substantially reduced, similar to the winding of a conventional AC contactor. As a result, the AC pickup winding can remain energized without burning out, although it is not required for maintaining the contacts in the closed positions thereof. The DC holding winding, on the other hand, is operative for maintaining the contactor in the closed position thereof; and since it operates on DC power, a dropout delay can be provided utilizing a capacitor. As a result, it is seen that the contactor of the instant invention combines the advantage of AC contactors with those of DC contactors to provide a reliable contactor having a delay-on-dropout feature. Further, although the invention is illustrated and described as a contactor, the embodiment thereof in solenoid relays, etc., is also contemplated.
Accordingly, it is a primary object of the instant invention to provide a reliable magnetically operable AC switching device having a delay-on-dropout feature.
Another object of the instant invention is to provide a reliable contactor having a delay-on-dropout feature which is energizable from an AC power source.
A still further object of the instant invention is to provide a switch for use with computer equipment to permit the safe shutdown thereof under power failure or severe brownout conditions.